Coal and biomass combustion has occurred for several millennia. However, commercial upgrading of combustion through the addition of combustion catalysts, increased oxygen or chemical oxidation of hydrocarbons became more widespread in the mid to late twentieth century and early twenty-first century. Combustion is the reaction of oxygen combining with carbon and hydrogen in the fuel in an exothermic reaction. Briefly, combustion catalysts are additives to the fuel that seek to generate more complete combustion of the hydrocarbons, or reduce problems with ash or emissions in the flue gas. Increased oxygen, oxygen over firing, or oxy-combustion all seek to increase the proportion of oxygen above the 20% in ambient air in order to improve combustion efficiency and reduce emissions. Chemical looping combustion employs a metal oxide to deliver oxygen for a chambered combustion reaction with hydrocarbons, and then recycles the metal for oxidation prior to looping back to the fuel reaction chamber. In general, depending on the nature of the raw coal and/or biomass in addition to the exact nature of the combustion process, the emissions from coal and biomass combustion generally contain large quantities of carbon dioxide and water vapor, and smaller emissions of acid gases, compounds of chlorine, mercury, additional heavy metals, hydrogen sulfide, and a wide range of inert ash material.
The history and detailed time-line of coal clean up through pyrolysis are well documented and found on a variety of websites. Details of a pyrolysis process can be found, for example, in “Kinetic Studies of Gas Evolution During Pyrolysis of Sub-bituminous Coal,” by J. H. Campbell et al., a paper published May 11, 1976 at the Lawrence Livermore Laboratory, Livermore, Calif. Numerous issued U.S. patents describe methods for the reduction of sulfur in coal, for example, U.S. Pat. No. 7,056,359 by Somerville et al. Their process involves grinding coal to a small particle size, then blending the ground coal with hydrated lime and water, followed by drying the blend at 300-400 degrees F. U.S. Pat. No. 5,037,450 by Keener et al. utilizes a unique pyrolysis process for denitrifying and desulfurizing coal. Here the sulfur and nitrogen content of coal is again driven off in gaseous form and sequestered for possible further use. Related art is described in U.S. Pat. No. 4,862,485, which teaches means for forming coal pellets by mixing coal particles with polyvinyl alcohol, calcium oxide and/or magnesium oxide and water. U.S. Pat. No. 4,738,685 teaches how to cold press coal fines with molasses, an inorganic hardening agent such as calcium carbonate, calcium phosphate, iron oxide, aluminum oxide or optionally with an acid. Additional teachings relevant, though differing from the present application can be found in U.S. Pat. Nos. 4,618,347, 4,586,936. 4,169,711 and U.S. Pat. No. 5,916,826. Patent application No. 20100162619 describes a method using a Mallard process at a pressure of 5 bar at an elevated temperature for compacting biofuels together with some limited amount of peat or lignite.
A more recent system has been proposed and published as USPTO application 20090020456 (Jan. 22, 2009) by Tsangaris et al, relating to the gasification of fossil fuels, fuels that are then used to process a variety of unconventional sources of oil sources such as tar sands and shale oil.
Additionally, in U.S. application Ser. No. 12/631,302, Lawrence F. McHugh et al instruct us in the oxidation of solid fuels via metallic oxide chemical looping, and points out that over time, minerals in the coal ash contaminate the oxygen carrier.
Chemical looping combustion (“CLC”) provides for the exothermic oxidation of hydrocarbons without ignition. Most CLC systems provide two chambers and a method of transporting grains of metallic oxide from one chamber to the other and then back to the first chamber, completing the loop. Metallic oxides are chosen for the ease with which they take on or give off an oxygen atom. For example, iron oxide is found in about 12 different forms, of which FeO and Fe2O3 are two common forms. In a CLC unit, one might find iron oxide grains in one chamber and pulverized coal or biomass, ground solid hydrocarbons, in the other chamber. When air is conveyed through the first chamber, FeO is converted into Fe2O3 in an exothermic reaction taking Oxygen atoms from the air. The grains of Fe2O3 are transported into the other chamber with ground solid hydrocarbons. In this second chamber, Fe2O3 is converted to FeO in a second exothermic reaction that combines hydrocarbons with oxygen to make water, H2O, and carbon dioxide, CO2. The iron oxide is then returned to the first chamber to be re-oxygenated. These paired exothermic chambers give off heat energy that is useful to do work for example, by the making of steam power. A pure CLC system uses pure oxygen from the air and pure hydrocarbons. When the hydrocarbons are not purified before CLC, then minerals in the coal and biomass that result in ash, may contaminate metallic oxide that serves as the oxygen carrier and result in lost efficiency and added processing cost.
The present application describes unique and novel systems and methods for obtaining calorically rich, nearly contaminant free combustibles for chemical looping combustion consisting of coal and biomass. The invention involves the preprocessing of the coal and biomass so resulting in major energy saving during the combustion stage, and preservation of the oxygen carrier free of contamination. The biomass can consist of algae, switch grass, wood matter, such as sawdust and/or wood chips, as well as manure to mention a non-exhaustive number of useful caloric components.
One of the several ways the present invention is particularly efficient is that it recovers and recycles the water vapor that is released from coal and biomass upon heating in a typical combustor. The fuel to be combusted which has already had the water removed makes the heat transfer of combustion considerably more efficient. At the same time, other contaminants such as S, H2S, Cl, Hg, As, Se and other minerals that have also been removed prior to CLC increases the efficiency and quality of the combustion process. Many of these impurities can then be recycled for further useful industrial applications. This form of recycling instead of disposal waste management is becoming recognized world wide as a necessary and achievable goal to reduce pollution and potential climate change.
The present invention is a further development of the work in the inventor's application Ser. No. 12/908,061 and is presented to make any claims different from said earlier application.
While some of the waste products from the burning of fossil fuels and biomass can be recovered or recycled, most are disposed of in landfill. This type of disposal is wasteful and in itself potentially polluting, clearly not an environmentally friendly or economical way to proceed. Various government agencies have now put laws into effect that make certain forms of this type of disposal illegal which can result in substantial fines.